1. Field of the Invention
The present invention relates to an electromagnetic switch apparatus available for a starter needed for driving an engine and also to a coaxial type starter which coaxially aligns an electromagnetic switch apparatus and a DC motor.
2. Description of Related Art
FIG. 1 illustrates a sectional view of main components of a conventional coaxial-type starter denoting the first conventional art disclosed in the Japanese Patent Application Laid-Open No. 1-238445 of 1989 for example. Referring to the following description, a DC motor shown to the right of FIG. 1 is positioned in the front, whereas an electromagnetic switch apparatus shown to the left of FIG. 1 is positioned in the rear, respectively.
The reference numeral 1 shown in FIG. 1 designates a DC motor incorporating the following: a relay iron member 2, a field pole 3 (a permanent magnet) which is secured to the relay iron member 2, a rear bracket 4, a brush holder 5 which is secured to the rear bracket 4, and an armature 6 which consists of the following; a hollow armature rotating shaft 7, an armature core 8 which is secured to the hollow armature rotating shaft 7, an armature coil 9 which is secured to the armature core 8, and a commutator 10 which is secured to the hollow armature rotating shaft 7 and connected to the armature coil 9. The rear end of the hollow armature rotating shaft 7 is held by the rear bracket 4 through a bearing unit 11; whereas the front end of this shaft 7 is held by a bearing holder integrated with the front end itself through a bearing unit (not shown). A front bracket 13 is coupled with the relay iron member 2. The front bracket 13 incorporates an epicyclic reduction gear which is engaged with a pinion (a sun gear) provided on the external circumference of the front end of the hollow armature rotating shaft 7. The front bracket 13 also incorporates an overrunning clutch which is engaged with the output part of the epicyclic reduction gear. The rear end of an output rotary shaft 15 is held by the hollow armature rotating shaft 7 through a sleeve bearing unit 16. The intermediate region of the hollow armature rotating shaft 7 is engaged with the overrunning clutch by a helical spline. The hollow armature rotating shaft 7 transmits rotating force to the output rotary shaft 15 in order to rotate a pinion 17 which is coupled with the front end of the output rotary shaft 15 by a spline. The pinion 17 starts to move forward by the forward movement of the output rotary shaft 15, and then the pinion 17 is engaged with a ring gear of the engine so that the engine can start up its operation.
The reference numeral 20 shown in FIG. 1 designates an electromagnetic switch apparatus which is coaxially coupled with the rear end of the DC motor 1. The electromagnetic switch apparatus 20 has the structure shown below. An exciting coil 21 is wound on a bobbin 22. A stationary core 23 is disposed in front of the exciting coil 21. A guide bush member 24 which is made from non-magnetic material and secured to the stationary core 23 is inserted in the internal circumference of the bobbin 22. A magnetic path case 25 made from magnetic material is coupled with the rear bracket 4 with surrounding the external periphery of the exciting coil 21. The magnetic path case 25 makes up a magnetic path core and secures the stationary iron core 23 thereto. A movable core 26 is held inside of the guide bush member 24 with facing to the stationary core 23 so that it can slidably move itself in the axial direction. The movable iron core 26 makes up a plunger and returns to the original position by effect of a compression spring 38. The rear end of a push rod 27 held by pressure of a coil spring 28 is placed inside of the movable core 26, whereas the front end of the push rod 27 presses the rear end of the output rotary shaft 15 through a steel ball 29.
A pair of stationary contacts 30 are secured by means of an insulating member 31 made from plastic material. A pair of terminal bolts 30a and 30b externally project themselves from those stationary contacts 30. A lead wire from a DC power-supply source (a battery) is connected to the terminal bolt 30a. Another lead wire 32 is connected to the terminal bolt 30b by means of a nut 33 so that the lead wire 32 can be extended to a brush unit. A movable contact 34 is held behind the stationary contacts 30 through a pair of insulating members 35a and 35b. A coil spring 36 is disposed between the movable core 26 and the insulating member 35a, where the coil spring 36 gives a contact pressure to the movable contact 34. A cover member 37 made from magnetic material is installed to the rear end of the magnetic path case 25.
FIG. 2 illustrates a sectional view of main components of a conventional coaxial-type starter denoting the second conventional art disclosed in the Japanese Patent Application Laid-Open No. 1-92573 of 1989 for example. Those reference numerals 1 through 11 and 13 through 17 shown in FIG. 2 respectively designate component members identical to those which are shown in FIG. 1.
The reference numeral 12 designates a bearing unit which is made available for holding the front end of the hollow armature rotating shaft 7. The reference numeral 20 designates an electromagnetic switch apparatus which is coaxially coupled with the rear end of the DC motor 1. The electromagnetic switch apparatus 20 has the structure shown below. An exciting coil 21 is wound on a bobbin 22. A stationary core 23 is provided in front of the exciting coil 21, whereas a rear core 18 is provided behind the exciting coil 21. A magnetic path case 25 made from magnetic material is coupled with the rear bracket 4 with surrounding the rear end and external circumference of the exciting coil 21. The magnetic path case 25 firmly secures the stationary core 23 and the rear core 18, where the magnetic path case 25 and the rear core 18 conjunctionally make up a magnetic path core. A guide bush member 24 which is made from non-magnetic material and secured to the stationary core 23 is inserted in the internal circumference of the bobbin 22. A movable core 26 is held inside of the guide bush member 24 with facing to the stationary core 23 so that the movable core 26 can slidably move itself in the axial direction. The movable core 26 makes up a plunger.
A pair of stationary contacts 30 are secured to the rear bracket 4 through an insulating member 31. A terminal bolt 30a extends from one of the stationary contacts 30. A lead wire (not shown) extended from a DC power-supply source (a battery) is connected to the terminal bolt 30a. A hollow rod 19 made from non-magnetic material is secured to the movable core 26. A movable contact 34 directly facing to these stationary contacts 30 is held by the hollow rod 19 with an insulating member 35 intervened. The hollow rod 19 is brought back to the original position by a return spring 39. The movable contact 34 is given a contact pressure by a compression spring 38. The rear end of a push rod 27 is held in the hollow rod 19 so that the push rod 27 can move itself in the axial direction. This push rod 27 is energized by a coil spring 28 and carried forward by the forward movement of the movable core 26, and then, the push rod 27 pushes the output rotary shaft 15 forward through a steel ball 29. Then, the steel ball 29 is energized by another coil spring 40 until it arrives at the innermost region of the rear end of the output rotary shaft 15. A spring shoe 41 is secured to the inner rear end of the hollow rod 19. A cover member 37 is coupled with the magnetic path case 25. Furthermore, the magnetic path case 25, the rear bracket 4, and the relay iron member 2, are engaged with the front bracket 13 by means of a through bolt 42.
Next, functional operations of the starter featuring the above structure are described below.
As soon as the starting switch of the engine is activated, DC power flows through the exciting coil 21, and then, the movable core 26 is attracted to the stationary core 23. As a result, the push rod 27 moves itself forward in order to push the output rotary shaft 15 in the forward direction, thus causing the pinion 17 to be engaged with the ring gear of the engine. Simultaneously, the movable contact 34 comes into contact with a pair of stationary contacts 30. As a result, a circuit connected to the armature coil 9 closes itself so that DC power can flow through it to activate rotation of the armature 6. Next, rotation of the armature rotary shaft 7 is reduced by the epicyclic gear unit, and then, the decelerated rotating force is transmitted from the output rotary shaft 15 to the pinion 17 through the overrunning clutch before eventually activating the rotation of the engine itself.
After turning the engine ON, the starting switch is turned OFF by the driver. Then, DC power supply to the exciting coil 21 is shut off, and then, the output rotary shaft 15 is brought back to the original position by effect of the return spring (not shown), thus disengaging the pinion 17 from the ring gear of the engine. Simultaneously, the movable core 26 is also brought back to the original position before the movable contact 26 eventually leaves a pair of those stationary contacts 30.
The above-cited conventional starter denoting the first conventional art provides a pair of stationary contacts 30 and the movable contact 34 at the rear end side of the magnetic path core, and as a result, a pair of those terminal bolts 30a and 30b projecting themselves in the radial direction from the external circumferential surfaces must compulsorily be disposed at the rear end side of the electromagnetic switch apparatus 20. Depending on the structure of the engine, positions of these terminal bolts 30a and 30b disturb subsequent operation to install the starter to the engine, and therefore yet, distribution of lead wire from the DC power supply source involves obstacle.
Furthermore, the rear end of the hollow rod 19 of the other conventional structure denoting the second conventional art is held by the guide bush member 24 of the movable core 26, and in addition, the intermediate region of the hollow rod 19 is held inside of the internal circumference of an insulating member 31 across a substantial gap. The insulating member 31 is held by the rear bracket 4. Since concentricity is variable by execution of assembly work, the substantial gap must be provided for the hollow rod 19. On the other hand, because of this substantial gap, the hollow rod 19 may incline itself, thus coming into contact with the internal circumferential surface of the hollow armature rotating shaft 7. This in turn causes the hollow rod 19 to also rotate with the shaft 7. Likewise, the movable contact 34 also starts to rotate itself, and as a result, the movable contact 34 cannot stably come into contact with the stationary contacts 30. Furthermore, metallic powder generated by the friction between the hollow rod 19 and the internal surface of the hollow armature rotating shaft 7 can easily enter into the contact chamber through the substantial gap between the insulating member 31 and the hollow rod 19. As a result, the abraded metallic powder easily adheres to the sliding surface of the contact chamber against the movable core 26, thus eventually obstructing the sliding movement between the surface of the contact chamber and the movable iron core 26 to lower the insulating effect against those contacts. Furthermore, grease of the bearing unit 11 may infiltrate into the contact chamber to obstruct proper contact between the movable contact 34 and the stationary contacts 30.